Manufacture of dicarboxylic acid esters of high polymer polyhydroxy compounds



Patented June 26,1945

MANUFAGIIUBE Q OF -DICABBOXYLIC ACID ESTEBS F 1 HIGH POLYMER POLYHY-.DBOXY COMPOUNDS Carl J. Main and La Moync D. Bearden, Roch-v aster, N.Y., assignors to Eastman Kodak Com pany, Rochester, N. Y., a.corporation of New Jersey No Drawings Application March 28, 1942, erialNo. 436,718

6 Claims. (01. 260-225) This invention relates to the preparation ofdicarboxylic acid esters of high polymer polyhydroxy compounds, in whichdilution is desirable before the precipitation step, in which trisodiumphosphate is added, thus enabling dilution with water. 7

The dicarboxylic acid esters or high polymer polyhydroxy compounds areordinarily prepared by treating either the polyhydrcxy compound on anester'or ether thereof, having free and esterifiable hydroxyyl groups,with a dicarboxylic acid anhydride under esterifying conditions; Thisesterification may be accompanied by the use of a tertiary organic basewith or'without a solvent, as shown in U. S. Patent No. 2,093,464, or inFordyce and Emerson application Serial No. 325,191, filed March 21,1940. On the other hand, the ester may be prepared by using a solventand employing an elevated temperature using an ester or ether of thepolyhydroxy compound as the starting material. In other cases esters ofthis nature may be prepared by melting together the vdicarboxylic acidanhydride and the hydroxy compound.

In those prior processes either the pyridine, the solvent or theirmixture were employed in large or excessive amount, as compared to thatnecessary to promote the reaction, orvelse it was necessary to dilutethe reaction mass with an organic solvent prior to its precipitation inorder to obtain a. finely divided readily worked precipitate and therebyassure the success of that separation step. The cost of the process wasincreased in any case because of the large proportion of solvent orpyridine employed.

In the making of the dicarboxylic acid esters of these polyhydroxycompounds, it is desirable to employ a minimum of solvent or pyridine orboth. as this makes for economy and also increases the concentration ofanhydride in the esteriflcation mixture. However, by thus decreasing theamount of liquid in the reaction mass, it is necessary to dilute itprior to precipitation. This may be done with an organic solvent but theeconomy achieved by restricting them of solvent in the esterification iscancelled by this further use of solvent. As the use of solvent withoutpyridine or a restricted amount of pyridine results in an ester which isinsoluble in water, water dilution would result in precipitation, of theester. The ester may be rendered soluble in water by adding trisodiumphosphate to the completed esterification mass, whereupon the mass maybe diluted to a thin consistency thereby iacilitating the precipitationof the ester.

Our invention is directed both to processes of preparing dicarboxylicacid esters of polyhydroxy compounds in which a restricted proportion ofpyridine is employed and those in winch pyridine is omitted entirely;For example, it has been found that, in the manufacture of dicarboxylicacid esters of.high polymer polyhydroxy compounds such as celluloseacetate phthalate, polyvinyl phthalate and the like, the amount orpyridine employed may be less than that which would combine with all ofthe carboxyl groups in the reaction mixture, providing a suitableauxiliary solvent is used and the reaction proceeds satisractorily. Therestricted proportion of pyridine results in a product which isinsoluble in water and to recover the product either the completedreaction mass should be diluted with an organic solvent or the productshould be rendered water soluble and the mass is then diluted with waterbeiore the precipitation. I

In some processes of making dicarboxylic acid esters of high polymerpolynydroxy compounds,

I the pyridine is omitted entirely. For instance,

Hiatt and Emerson Patent No. 2,352,261, de-

scribes a method of making such esters in which the dicarboxylic acidanhydride and the hydroxy compound are melted together. In such aprocass, in accordance with our invention, the completed reaction massis diluted with an aqueous solution of trisodium phosphate and theproduct can then be separated from the mass by precipi-H tatins indilute acid.

In some processes of making dicarboxylic acid esters or high polymerpolynydroxy compounds, the polyhydroxy compound is reacted with theanhydride oi the diCflIbOlLYli-C acid in an organic solvent containing asmall proportion of water, using an elevated temperature as described inU. S. patents, No. 2,183,982 of Blanchard and Crane and No. 2,275,685 ofMartin Salo. The products resulting from processes of that type areinsoluble in water but soluble in organic solvents and heretofore eitherthe amount of solvent employed in the esterification mad dilutionunnecessary before precipitation or an organic solvent was added to thecompleted reaction mass to facilitate that operation. In accordance'withour invention the completed reaction mass is diluted with an aqueoussolution of trisodium phoshydrochloric, sulfuric or phosphoric acid of5% efiective concentration.

In its broadest aspects, our invention comprises adding trisodiumphosphate to the completed reaction mixture in an amount sufilcient toneutraliz all of the free carboxyls therein. This applies to processesfor making cellulose acetate phthalate, cellulose phthalate, polyvinylphthalate, cellulose acetate succinate, or in general, acid dicarboxylicacid esters Of high polymer polyhydroxy compounds. We have found that asolution of trisodium phosphate in water is quite satisfactory forimpartin water solubility to the ester without hydrolyzingit or causingexcessive foaming as might be caused by the use of sodium hydroxide orsodium carbonate. After the addition of the trisodium phosphate to thecompleted reaction mixture, water as a diluent may be added until themas has the desired viscosity. Obviously when a high viscosity ester isprepared, more dilution would be desirable than with a low viscosityester.

The following examples illustrate our invention:

Example I 50 pounds of a hydrolyzed cellulose acetate containing 33.5%acetyl was dissolved in a mixture of 50 pounds of pyridine and 50 poundsof methyl ethyl ketone. 50 pounds of phthalic anhydride was addedthereto and the mass was stirred and kept at a temperature ofapproximately 180 F. for two and one-half hours. The mass was cooled to145 F. and 54 pounds of acetone were added thereto. The mass was thencooled to room temperature and 120 pounds of 10% trisodium phosphate wasadded slowly with stirring. The mass was then diluted with 60 pounds ofdistilled water and 12 gallons of the mass was precipitated into 80gallons of distilled water to which five pounds of 95% sulfuric acid hadbeen added. The product was thoroughly washed and dried. The resultingproduct was a cellulose acetate phthalate having a phthalyl content of30.0%.

Example II 75 pounds of cellulose acetate, containing 38.5% acetyl andfree and esterifiable hydroxyl groups, was thoroughly mixed in anautoclave with 75 pounds of methyl ethyl ketone, 75 pounds of phthalicanhydride and seven pounds of distilled water. The mass was heated andmixed together for five hours. The heating consisted of raising thetemperature to 300 F. gradually during the first three hours and thenmaintaining at 300 F. for the remainder of the time. The mixture wasthen cooled to 130 F. 120 pounds of a solution of trisodium phosphate inwater of 10% concentration was added to the mass which was warmed to 100F. and stirred for 10 minutes. Six gallons of the mixture wasprecipitated into 110 gallons of water to which five pounds of sulfuricacid had been added. The mass was thoroughly washed and dried. Acellulose acetate phthalate containing 22% phthalyl was obtained.

Example III 450 grams of phthalic anhydride was mixed with 480 grams ofmethyl ethyl ketone and 270 grams of pyridine for one hour atapproximately 130 F. 150 grams of polyvinyl alcohol was added and thereaction was carried out at 220 F. for five hours. The mass was thencooled to l60-180 F. and was diluted with four pounds of a 10% solutionof trisodium phosphate in water. The

content of 38.5

mass was then diluted further with 1500grams of distilled waterand wasprecipitated into 10 gallons of water containing 1135 grams oi sulfuricacid. The ester was thoroughly washed and dried. A polyvinyl phthalatecontaining 68% phthalyl resulted.

In precipitating the dicarboxylic acid ester in aqueous acid, the acidshould be present in the precipitating bath in such amount that itremains acid thruout the precipitation. For instance if an amount ofsodium phosphate greater than necessary has been employed in thediluting step more acid than ordinarily necessary snould be employed inthe precipitating bath to compensate therefor. Altho our invention hasbeen described using trisodium phosphate, disooium or monosodiumphosphates can be used, the amount of the former required being 1 timesthat of trisodium phosphate while the amount of the latter required is 3times the preferred trisodium compound. Trisodium phosphate proves to bethe most economical of any of the phosphates which can be employed.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

l. A process for the manufacturing of a dicarboxylic acid ester ofcellulose which comprises reacting upon a cellulose acetate having freeand esterifiable hydroxyl groups with a dicarboxylic acid anhydride inwhich any pyridine present is in an amount substantially less than thatwhich will combine with the carboxyls present in the cellulose esterformed, then adding trisodium phosphate to the mass in an amount atleast sutiicient to neutralize the free carboxyl groups of the esterformed and subsequently separating the ester by mixing the mass with aprecipitating liquid essentially consisting of an aqueous solution of amineral acid, the precipitating bath being acid throughout theprecipitation.

2. A method of manufacturing cellulose acetate phthalate which comprisesreacting cellulose acetate having free and esterifiable hydroxyl groupswith phthalic anhydride in which any pyridine present is in an'amountsubstantially less than will combine with the carboxyl groups of thecellulose ester formed, after the esterification is completed addingtrisodium phosphate to the mass in an amount suflicient to neutralizethe free carboxyl groups of the ester formed and subsequently separatingthe ester from the mass by mixing with a precipitating liquidessentially consisting of water and a mineral acid, the precipitatingbath being maintained acid throughout the precipitation.

3. A method of manufacturing cellulose acetate phthalate which comprisesreacting cellulose acetate having free and esterifiable hydroxyl groupswith phthalic anhydride, the esterification mass being substantiallyfree of pyridine, adding trisodium phosphate to the completed reactionmass in an amount sufiicient to neutralize the free carboxyl groups ofthe ester and subsequent- 1y separating the ester from the mass bymixing with a precipitating liquid essentially consistin of water and amineral acid, the precipitating bath being maintained acid throughoutthe precipitation.

4. A process for the manufacture of a dicarboxylic acid ester ofcellulose which comprises reacting upon a cellulose acetate having anacetyl per cent and free and esteriflable hydroxyl groups with adicarboxylic acid anhydride in which any pyridine present is in anamount substantially less than that which will combine with thecarboxyls present in the cellulose ester formed, then adding trisodiumphosphate to the mass in an amount at least sufilcient to neutralize thefree carboxyl groups of the ester formed and subsequently separating theester by mixing the mass with a. precipitating liquid essentiallyconsisting of an aqueous solution of a mineral acid, the precipitatingbath being acid throughout the precipitation.

5. A process for the manufacture of cellulose acetate phthalate whichcomprises reacting cellulose acetate having free and esterifiable groupswith phthalic anhydride and a restricted proportion of pyridinesubstantially less than that which would combine with the carboxylspresent in the cellulose ester formed adding trisodium phosphate to thecompleted reaction mass in an amount sufiicient to neutralize the freecarboxyl groups of the ester and subsequently separatin the ester fromthe mass by mixing with a precipitating liquid essentially consisting ofwater and. mineral acid, the precipitating bath being maintained acidthroughout the precipitation.

6. A process for the manufacture or a dicarboxylic acid ester ofcellulose which comprises reacting upon a cellulose acetate having freeand esteriflable groups with a dicarboxylic acid anhydride in which anypyridine present is in an amount substantially less than that which willcombine with the carboxyls present in the cellu-- lose ester formed,then adding trisodium phosphate in the form of a 10 per cent aqueoussolution thereof to the mass in an amount at least sufllcient toneutralize the free carboxyl groups of the ester formed and subsequentlyseparating the ester by mixing the mass with a precipitating liquidessentially consisting of an aqueous solution 01' a mineral acid, theprecipitating bath be- CARL J. MALM. LA MOYNE D. BEARDEN.

